3 Answers
3

I know for certain the level trophies are unlockable in DA DLC, for example when starting the Witch Hunt DLC, your main character will be on level 20 and will instantly unlock the respective class trophy, even though it's a "main game" trophy. I don't know about the Heavy Hitter trophy, but I'll assume it unlocks on DLC as well.

The "kill darkspawn" trophies are another issue, though, it seems patches to the game have messed with the kill counters and rendered these trophies glitched in some cases, I would recommend reading this guide regarding these trophies. He does mention on the guide that these in fact

Thanks for that guide. I hadn't noticed that you could reload & increase the count. I had (incorrectly it seems) figured it was probably linked to the save file & not the character. Looking at that guide I may be better getting rid of the patches & just doing the remaining origins as it allows the count over multiple characters (before playing Awakening).
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ItsPeteJun 7 '12 at 1:21

I can confirm from my experience that both Heavy Hitter and Archmage can be unlocked in Awakening. They're easier to unlock too. Archmage can be gotten instantly as in JohnoBoy's answer. And since you can start with points in the skills that do the most damage, e.g. Arrow of Slaying or Mana Clash, Heavy Hitter can be unlocked fairly early as well.

Regarding Master Warden/Blgiht Queller, according to various achievement forums, they are definitely earnable in Awakening. Note that the kills have to be by the warden main character, however and not by the whole party. At least on the PS3, it seems that loading a save does not reset the counter, so they can be earned by replaying a chosen battle over and over.

Heavy Hitter can be achieved with an archer since in Awakening a well built max level archer hits for around 250 damage per shot. Walking Bomb with a well built spellpower mage can also cause it to pop around level 14 or so in the base game.